For years, omnidirectional outdoor warning sirens have been available which consist of multiple horns mounted in back-to-back circular arrays. These sirens exhibit lobing problems in their coverage patterns, however, due to cancellation and/or addition of sound waves emanating from the multiple sources. Consequently, rotation of such arrays is necessary to ensure total area coverage.
More recently, omnidirectional modular sirens have become available through companies such as Whelen Technologies, Inc., and Kockum Sonics. Those sirens consist of a plurality of stacked, disc-shaped modules, each active module having an orifice in either its lower or upper surface through which sound waves--generated by an interiorly mounted compression driver/horn assembly--pass and then spread out omnidirectionally. Whelen's sirens have a single driver/horn assembly per active module, with each driver/horn assembly mounted vertically within a module and directed toward an upper orifice. Since only one driver is used in each module by Whelen, each driver must be very powerful (typically 400 watts) and is, therefore, quite expensive. Kockum Sonics, a Swedish company, manufactures sirens having 1-3 drivers per active module, but the specific arrangement of the drivers and their respective horn assemblies within the modules is presently unknown to applicant.
The vertical stack of modules making up a Whelen siren is coupled together by means of an assembly consisting of a plurality of exteriorly mounted, aluminum cast spacers and annular members (as shown in U.S. Design Pat. NO. 305,660) and the Kockum Sonics modules are coupled by means of a plurality of tie rods and spacers. Access to a driver housed within a module, such as for repair or replacement, is possible in either a Whelen or Kockum Sonics siren only by disassembling the module, thus requiring disassembly of all or part of the coupling assembly. Such disassembly, of course, is quite time consuming and costly.